Although the three calculations jotted on the back of a piece of paper do not look like much, the neat rows of black figures offer an elegantly brutal precis of one of the most remarkable lives of the 20th century.

The first reveals the number of years the writer spent in prison (28); the second, how old he was when the law caught up with him (44), and the third, the age at which he was released (72).

The sums would be of scant interest were it not for the fact that the man measuring out his life in ink that day was Nelson Rolihlahla Mandela.

That page – and thousands more belonging to the former South African president – are now at the centre of a bidding war as international publishers scrabble to acquire the rights to a book based on Mandela's private archive.

While the private collection of journals, diaries, letters, speeches, notebooks and personal reflections has yet to be distilled into a book, the raw archive materials seem likely to take this week's Frankfurt book fair by storm.

Mandela himself, who bestowed these "traces of my life and those who have lived it with me" on his eponymous foundation, hopes the collection will afford the world a glimpse into his mind and his past.

"Anyone who has explored the world of archives will know that it is a treasure house, one that is full of surprises, crossing paths, dead ends, painful reminders and unanswered questions," he said.

Jonny Geller, an agent at the Curtis Brown literary agency and the man entrusted with handling the book's worldwide rights, described the collection on offer as an "utterly remarkable" resource.

"I've never heard of a living political leader giving up their entire archive," he said as he waited for his plane to Frankfurt. "I can't think of any other political leader who has opened up their archive without any censorship.

"There's everything from political scribblings to letters to his wife. It's an incredible archive, which will not only have political and historical insights, but which will also provide an emotional insight into the man too. It will give a portrait of the man and his life."

Verne Harris, acting head of the Nelson Mandela Foundation, said the documents afforded "unique access to Madiba in his private moments, his personal reflections in response to circumstance that helped him to the daily disciplines, the life lessons and to the moral and political vision which inspired, and continues to inspire so many".

According to Geller, the Mandela who emerges from the archive is a flesh-and-blood man and a prolific letter-writer.

"He has notebooks from Robben Island [where Mandela was imprisoned] which are absolutely packed with his handwriting. And he kept drafts of letters he sent, most of which never got through. There's scraps of paper with his notes on leadership."

There is also, in one of the less predictable epistolary partnerships, a letter discussing the role of police in society set down on notepaper emblazoned with both the legend From the Desk of Nelson Mandela and the image of the rotund and lasagne-loving cartoon cat Garfield.

Geller describes the book as "a look behind Long Walk to Freedom", the autobiography that Mandela published in 1995, and which has sold more than 6m copies around the world.

The agent would not discuss how much Macmillan UK had paid for the British and Commonwealth rights, nor speculate on how much the US rights could go for. But he did confirm there had already been offers from eight territories.

Asked how he expected the week's bidding to go in Germany, Geller said: "It's going to be a book that will take over the Frankfurt book fair and become the book of the fair."

According to the Bookseller, which broke the news of the archive's publication, the British book will be called Conversations with Myself and will be published next year to mark the 20th anniversary of Mandela's release from prison.

A new biography, Young Mandela, charting Mandela's life in the early 1960s before his imprisonment, will also be published next year to coincide with the anniversary and the start of the World Cup in South Africa.

Although it remains to be seen what revelations the archive will yield, its 91-year-old creator should not have too much trouble finding favourable blurbs for the book jackets.

Archbishop Desmond Tutu has already described Mandela as "a gift to the world", while Hillary Clinton, who has seen the archive, might also be worth tapping for a quote.

"[It] will be a treasure trove of information, of memories, of lessons and guidance for generations to come," said the US secretary of state on a recent trip to Africa.

"You can see in the recording of his days, what he was doing, what he was thinking – in the discipline that he brought to a life filled with so many great achievements, not only for him personally but for South Africa and the world."